Add explicit line about source build via pip. (#228)

Summary:
As title.

Pull Request resolved: #228

Test Plan: N/A.

Reviewed By: PaliC

Differential Revision: D40683724

Pulled By: anirbanr-fb-r2p

fbshipit-source-id: b4e3f090d3a8da87b5aa3e8890f1c9b8e2d58ba4

Author: anirbanr-fb-r2p

README.md

@@ -32,9 +32,9 @@ docker run --rm multipy multipy/runtime/build/test_deploy
 
 ### Installing via `pip install`
 
-We support installing both python modules and the runtime libs using `pip install`, with the caveat of having to manually install the dependencies first.
+We support installing both python modules and the runtime libs using `pip install`, with the caveat of having to manually install the C++ dependencies first. This also serves as a single-command source build, essentially being a wrapper around `python setup.py develop`, once all the dependencies have been installed.
 
-To start with, the multipy repo should be cloned first:
+To start with, the multipy repo should be cloned:
 ```shell
 git clone https://github.com/pytorch/multipy.git
 cd multipy